A fluid-driven impactor is one of BHA (Bottom Hole Assembly) tools powered downhole in rotary drilling processes and rotary-impacting drilling is a new process with respect to the prior art. The operation principle of the rotary-impacting drilling is as follows: a fluid-driven impactor is provided at the top of a bit or a core barrel. During the drilling, the bit rotates along with a drill string under a given bit pressure. In the meantime, the drilling bit is subjected to high frequency impacts from the impactor, such that the rock is broken under the joint action of the rotary motion and the impact motion so as to substantially increase the drilling penetration rate.
In CN 2385068Y is disclosed a fluid-driven impactor which, as shown in FIG. 1, comprises: an upper joint 1; an outer sleeve 2 connected to a lower threaded portion of the upper joint I at its upper end; a middle joint 3 connected to a lower threaded portion of the outer sleeve 2 at its upper end and provided with a central passage; an outer pipe 4 connected with a lower end of the middle joint 3 via thread; an inner-prismy sleeve 5 having an inner hole with a polygonal profile and connected to a lower threaded portion of the outer pipe 4 and provided with a central passage; an anvil 6 mounted inside the sleeve 5 and provided with outer threads at the lower end thereof; a lower joint 7, having, at the upper end thereof, a hole with an inner thread to which is connected the lower end of the anvil 6, and having, at the lower end thereof, a threaded hole for mounting tools such as drilling bit. In the impactor, the central passage of the middle joint is in communication with an inner cavity of the outer pipe. An upper fluid-diverging lid 8 with a central hole and a plurality of fluid-diverging holes, a jet element 9 with a plurality of outlet holes 90, a cylinder 10 with an inner cavity, a piston 11 mounted in the inner cavity of the cylinder 10, a piston rod 12 connected to the piston 11, a lower cylinder lid 13 mounted at the bottom end of the cylinder 10 and provided with a central hole for passing the piston rod 12 and an impacting hammer 14 connected to the piston rod 12 and having impacting action on the top of the anvil 6 are in sequence mounted in the outer sleeve 2, the middle joint 3 and the outer pipe 4. The fluid undesired for the impacting operation will be drained out through the fluid-diverging holes in the upper fluid-diverging lid 8 so as to join in the drilling circulation. The inner cavity of the cylinder 10 is divided into an upper cavity 15 and a lower cavity 16. One of these outlet holes of the jet element 9 is in communication with the lower cavity 16 by means of a side cavity passage 17. The inner wall of the outer sleeve 2 and the outer wall of the cylinder 10 define the borders for the side cavity passage 17. In other words, the side cavity passage 17 is formed between the inner wall of the outer sleeve 2 and the outer wall of the cylinder 10 in such a way that a slot with a C-shaped cross section is made in the outer wall of the cylinder 10, the slot opening to the inner wall of the outer sleeve. The description of the jet element 9 is omitted for clarity, since it is known in the art and has been described for example in CN 2385068Y.
The operation of the fluid-driven impactor is described as follows:
The working fluid from the central hole of the upper fluid-diverging lid 8 enters the upper cavity 15 and lower cavity 16 through the jet element 9 and its outlet holes. The piston 11 and further the piston rod 12 and the impacting hammer 14 reciprocate inside the cavities under the pressure difference between the upper cavity 15 and lower cavity 16, in order to transmit the impacting force to the top of the anvil 6, the lower joint and thereby the drilling bit. In the meantime, the torque from the drilling string is transmitted to the anvil 6, then to the lower joint 7 and the drilling bit through the inner-prismy sleeve 5, thereby enabling a drilling member such as a drilling bit connected to the lower joint to drill forward under the action of the rotary force and impacting force. Such a fluid-driven impactor can substantially improve drilling efficiency and meanwhile reduce the drilling cost. Generally, the power transmission mechanism of the impactor comprises the anvil, the inner-prismy sleeve and the lower joint.
However, there are some disadvantages with the fluid-driven impactor and its power transmission mechanism disclosed in CN 2385068Y.
First, the abrasive members in the fluid-driven impactor need to be replaced due to the abrasion, which shortens the working life of the fluid-driven impactor. There are two abrasive members: the fluid-diverging holes in the upper fluid-diverging lid and the O-shaped rubber seal ring located between the outer surface of the cylinder and the inner wall of the outer sleeve. The O-shaped rubber seal ring is used for sealing the side cavity passage to allow the fluid from the jet element to enter the lower cavity of the cylinder. The O-shaped seal ring is referred as the primary seal, whose working life, in practice, is less than 30 hours and therefore the working life of the fluid-driven impactor is less than 30 hours.
The reason why the rubber seal ring (the primary seal) is liable to abrasion is that the flow rate of the drilling fluid passing by the seal ring is very high and the shapes of various components are irregular, which causes swirl or vortex to directly flush the seal ring abrasively. Moreover, the primary seal prematurely degrades or damages due to the high temperature and pressure of the corrosive downhole drilling fluid and due to flush and corrosion of the main internal parts. In addition, the reason why the fluid-diverging hole is liable to abrasion is that the upper fluid-diverging lid is made generally of a structural steel alloy with a relatively low hardness as HRC of 28 to 32, for example 40Cr and 35CrMo. Therefore, the high-speed fluid easily flushes the holes abrasively. In general, the working life of the fluid-diverging hole is about 30 hours.
Second, the fluid-driven impactor does not increase the drilling speed significantly, since when the impacting power is transmitted to the bit, 60% of the impacting power is lost, that is, only 40% is applied to the drilling bit. Therefore, the working efficiency for drilling in both impacting and rotary way is greatly reduced.
Finally, the upper fluid-diverging lid has to be often replaced, because the fluid-diverging holes as described above are liable to abrasion, and the size of the fluid-diverging holes are fixed, such that for handling different flow of fluid, the fluid diverging holes need to be re-processed to have different sizes, or a series of upper fluid-diverging lids having fluid diverging holes of varying sizes must be prepared. Therefore, the cost for maintaining the upper fluid-diverging lids is increased yet the efficiency is not improved.
The above disadvantages can severely affect and restrain the working life and efficiency of the fluid-driven impactor, and thereby affect broad applications of the rotary-impacting drilling technique and the economic and technological benefits.